Battery-Powered Freezer Alarm - A typical freezer can contain hundreds of dollars with of food. if the device becomes unplugged or if the door is left open too long, the food inside can quickly become spoiled. The hobby circuit below is a battery powered alarm system, which is attached . . . Hobby Circuit designed by Dave Johnson P.E.-July, 2006

Cooling Fan Thermostat (12v) - This circuit will turn on a 12v DC powered cooling fan when the air temperature reaches a certain high temperature and will keep the fan turned on until the temperature drops below a second lower level. Both the high and low temperatures are both adjustable . . . Hobby Circuit designed by David A. Johnson P.E.-February, 2011

Freeze Alarm - I chose an accurate thermistor from Keystone as the temperature sensor for this circuit. This device has a very specific resistance at a particular temperature. According to the data sheet for the thermistor, the device will have a resistance of 361K at zero degrees C, which is the freezing point of water. The thermistor is wired into a simple bridge circuit, which uses 1% resistors. The bridge is connected to a very low power voltage comparator. The circuit forms a switch circuit, which changes state, when the resistance of the thermistor reaches a certain value. At zero degrees C the voltage at the non-inverting input of the comparator exceedsCircuit Solution by David A. Johnson P.E.-May, 2006

Freezer Over-Temperature Alarm - This circuit turns on a beeper whenever the inside temperature of a freezer is greater than zero degrees Centigrade. The circuit draws only a few microamps from a 9 volt battery. it uses a glass bead thermistor accurate to 1 degree C.. . . Circuit by David Johnson P.E.-November, 2014

Freezing Temperature Alarm - The circuit below is designed to activate a beeper alarm, whenever the outside air temperature is below 0 degrees C (32F). A 9v battery powers the circuit. The average 9ua current is so low that the battery should last for many years.. . . Circuit by David A. Johnson P.E.-November, 2014

Battery-operated remote-temperature sensor drives 4- to 20-mA current loop - 12/17/04 EDN Design Ideas: You can remotely measure temperature using a 4- to 20-mA current loop as long as 4000 feet and a battery-powered, white-light LED driver. You usually configure this equipment to provide a programmable, constant current to an LED from a battery source. The TPS62300 series of IC s, for example, converts a battery voltage of 2 __ Circuit Design by Scot Lester, Texas Instruments, Dallas, TX

Battery-Powered Freezer Alarm - A typical freezer can contain hundreds of dollars with of food. if the device becomes unplugged or if the door is left open too long, the food inside can quickly become spoiled. The hobby circuit below is a battery powered alarm system, which is attached . . . Hobby Circuit designed by Dave Johnson P.E.-July, 2006

Celsius-to-digital thermometer works with remote sensor - 04/15/04 EDN Design Ideas: You can use a single-supply system to precisely measure the temperature at a remote location with less than 1°C error over a 0 to 100°C range (Figure 1). The circuit includes T1, a low-cost AD590 temperature sensor; IC 1, an AD8541 r __ Circuit Design by Elana Lian and Chau Tran, Analog Devices, Wilmington, MA

Circuit Improves On Earlier Idea - EDN Design Ideas: 05/24/2012 A self-biasing thermistor circuit had an overall dominant thermal/electrical time constant as small as 25 msec but had a significantly rounded response following a square (thermal) input pulse of 100 msec; the source was a pulsed blue LED. A single-op-amp-based “anticipator-like” circuit generated a more faithful picture of the actual input excitation, and improved on the circuit described in a previous Design ideas (Reference 1). The lowpass filter in Figure 1, with an RC time constant of approximately 25 msec, models the circuit. __ Circuit Design by Nicholas Lockerbie, Scottish Universities Physics Alliance, Glasgow, Scotland

Circuit Linearizes, Converts Thermistor Data - 12/07/95 EDN Design Ideas: Although the response of thermistors is inherently nonlinear, you can make the devices' resistance over a selected range of temperatures linear. You can convert the thermistor value to a voltage for display on either a DMM or a panel meter. The circuit in Figure 1 performs linearization and provide as gain and offset for a YSI 44031 thermistor, whose nominal resistance is 10 k[ohm] at 25ºC. __ Circuit Design by Matthew Beckner, Ball Corp Boulder, CO

Circuit provides Cold-Junction Compensation - 11/28/02 EDN Design Ideas: The accuracy of any circuit or system that uses a thermocouple to determine the temperature of a process is limited by the accuracy of the method used to perform cold-junction compensation. in a thermocouple measurement, two wires __ Circuit Design by Mark Maddox, Analog Devices, Wilmington, MA, and John Wynne, Analog Devices, Limerick, Ireland

Cold Activated Switch - The thermistor used has a resistance of 15k at 25 degrees and 45k at 0 degrees celsius. A suitable bead type thermistor is found in the Maplin catalogue. The 100k pot allows this circuit to trigger over a wide range of temperatures. A slight amount of hysteresis is provided by inclusion of the 270k resistor. This prevents relay chatter when temperature is near the switching threshold of this circuit __ Designed by Andy Collison

Complete Type K Thermocouple Measurement System (SPI) with Cold Junction Compensation - The LTC2484 is ideal for direct digitization of thermocouples and other low voltage output sensors. The input has a typical offset error of 500nV (2.5μV max) offset drift of 10nV/°C and a noise level of 600nVRMS. The only signal conditioning is a simple surge protection network. in any thermocouple meter, the cold junction __ Linear Technology/Analog Devices App Note, Apr 8th 2010

Computer Voltage & Temperature Monitoring - The LTC2991 is used to monitor system temperatures, voltages and currents. Through the i2C serial interface, the eight monitors can individually measure supply voltages and can be paired for differential measurements of current sense resistors or temperature sensing transistors. Additional measurements include internal temperature __ Linear Technology/Analog Devices App Notes, Sep 7th 2011

Cooling Fan Thermostat (12v) - This circuit will turn on a 12v DC powered cooling fan when the air temperature reaches a certain high temperature and will keep the fan turned on until the temperature drops below a second lower level. Both the high and low temperatures are both adjustable . . . Hobby Circuit designed by David A. Johnson P.E.-February, 2011

Crystal heater / temperature stablization (TXCO) - OK, here is the circuit I used - See image below. The original National Semiconductor circuit had a 30 K resistor in series with a 400 µF cap., both in parallel with the 100 K resistor on the input of the 1st LM324 section. I found that combo to actually destabilize the operation of the controller for this particular application, so I removed them & changed the 2 µF cap in series with the 10 megohm resistor to 5 µF.__ Bobengler NO6B

Differential Bridge Amplifier - The LTC2050HV are zero-drift operational amplifiersavailable in the 5- or 6-lead SOT-23 and SO-8 packages. The LTC2050 operates from a single 2.7V to 6V supply. The LTC2050HV operates on supplies from 2.7V to ±5.5V. The current consumption is 800μA and the versions in the 6-lead SOT-23 and SO-8 packages offer power shutdown __ Linear Technology/Analog Devices App Note, Apr 29th 2010

Digital Remote Thermometer - This circuit is intended for precision centigrade temperature measurement, with a transmitter section converting to frequency the sensor's output voltage, which is proportional to the measured temperature. The output frequency bursts are conveyed into the mains supply cables. The receiver section counts the bursts coming from mains supply and shows the counting on three 7-segment LED displays. The least significant digit displays tenths of degree and then a 00.0 to 99.9 °C range is obtained. Transmitter-receiver distance can reach hundred meters, provided both units are connected to the mains supply within the control of the same light-meter. __ Learning Electronics

Digital Remote Thermometer - This circuit is intended for precision centigrade temperature measurement, with a transmitter section converting to frequency the sensor's output voltage, which is proportional to the measured temperature. The output frequency bursts are conveyed into the mains supply cables. The receiver section counts the bursts coming from mains supply and shows the counting on three 7-segment LED displays. The least significant digit displays tenths of degree and then a 00.0 to 99.9 °C range is obtained. Transmitter-receiver distance can reach hundred meters, provided both units are connected to the mains supply within the control of the same light-meter. __ Contact Flavio Dellepiane, fladello @ tin.it

Digital Thermometer - This digital thermometer can measure temperatures up to 150C with an accuracy of +_1C. The temperature is read on a 1V full scale-deflection (FSD) moving-coil voltmeter or digital voltmeter. Operational amplifier IC ...__ Electronics Projects for You

Digital Thermometer Sends Data over AC Power Line - This circuit is intended for precision centigrade temperature measurement, with a transmitter section converting to frequency the sensor's output voltage, which is proportional to the measured temperature. The output frequency bursts are conveyed into the mains supply cables. The receiver section counts the bursts coming from mains supply and shows the counting on three 7-segment LED displays. The least significant digit displays tenths of degree and then a 00.0 to 99.9 °C range is obtained. Transmitter-receiver distance can reach hundred meters, provided both units are connected to the mains supply within the control of the same light-meter. __ Contact Flavio Dellepiane, fladello @ tin.it

Digital Thermometer/Thermostat - it covers the range from -55 °C to 1200°C and has an over or under temperature alarm and switched outputs for thermostatic control.__ SiliconChip

Digital Thermometer-Cum-Controller - This standalone digital thermometer controls the temperature of a device according to its requirement. it also displays the temperature on four 7-segment displays in the range of –55°C to +125°C. At...__ Electronics Projects for You

Digital Thermostat with LED Temperature Display - I needed to replace two old, unreliable thermostats for controlling the heating and cooling for a large garden shed. Commercial basic digital thermostats are available quite cheaply, but some lack the ability to control heavy loads or have the extra features that I require for saving energy when the door is often left open or to indicate temperature being out of range etc. I like the PIC 18F1320 microcontroller used in my previous project, so decided to use it again in a very similar design to drive three multiplexed LED displays and read the temperature from a Dallas/DS18x20 "1-Wire" digital sensor. __ Designed by D. Thorpe, 2006

Digithermo 0-100.0 °C - Build your own a laboratory instrument for measuring time and temperature. The DigiThermo demonstrates the use of 'C' language, a dual-slope converter, LCD interfacing, and digital filtering as well. __ Designed by Wichit Sirichote

Diode Serves as a Sensor for a Thermal Probe - 02/16/12 EDN Design Ideas: A two-transistor thermal probe can be used to diagnose circuit problems, such as hot components and thermal runaway. __ Circuit Design by Raju Baddi, Tata Institute of Fundamental Research, Pune, India

DPPs make nonvolatile microvolt DAC - 31-Oct-02 EDN Design Ideas: The availability of a seemingly limitless variety of monolithic DAC chips makes it easy to implement most digital-to-analog-conversion applications with a single off-the-shelf device. Sometimes, an unusual set of requirements necessitates a multichip approach, however. One example of such a requirement is the need for nonvolatility of the DAC's setting in power-up and -down cycles __ Circuit Design by Stephen Woodward, University of North Carolina, Chapel Hill, NC

Electronic Thermostat for Fridge - A thermostat is a standard equipment for sensing temperature of a system and maintaining it at a pre-defined point. it is a regular feature in air-conditioners, room heaters and refrigerators. Although...__ Electronics Projects for You

Four Temperatures 8 digit LED termometer, using PIC16 & LM50B - Since I started my watercooling prejoect, I have been verry interested in how well it perform,
the only way is to measure all temperatures before and after,
The motherboard temperature sensors is useless unacurate, so i'm using LM50B. By using this LM50B sensor I get 1 C of real accuracy I use a PIC 16F876 to drive a four two digits LED displays, the PIC 16 has 4 analog inputs with 10 bits resolution, now I can display 4 temperatures at the same time to monitor performance :-) I monitor CPU, Chipset, GFX card, Harddisks. __ Designed by Thomas Scherrer OZ2CPU

Freeze Alarm - I chose an accurate thermistor from Keystone as the temperature sensor for this circuit. This device has a very specific resistance at a particular temperature. According to the data sheet for the thermistor, the device will have a resistance of 361K at zero degrees C, which is the freezing point of water. The thermistor is wired into a simple bridge circuit, which uses 1% resistors. The bridge is connected to a very low power voltage comparator. The circuit forms a switch circuit, which changes state, when the resistance of the thermistor reaches a certain value. At zero degrees C the voltage at the non-inverting input of the comparator exceedsCircuit Solution by David A. Johnson P.E.-May, 2006

Freezer Over-Temperature Alarm - This circuit turns on a beeper whenever the inside temperature of a freezer is greater than zero degrees Centigrade. The circuit draws only a few microamps from a 9 volt battery. it uses a glass bead thermistor accurate to 1 degree C.. . . Circuit by David Johnson P.E.-November, 2014

Freezing Temperature Alarm - The circuit below is designed to activate a beeper alarm, whenever the outside air temperature is below 0 degrees C (32F). A 9v battery powers the circuit. The average 9ua current is so low that the battery should last for many years.. . . Circuit by David A. Johnson P.E.-November, 2014

Frost Alarm - The thermistor used has a resistance of 15k at 25 degrees and 45k at 0 degrees celsius. A suitable bead type thermistor is found in the Maplin catalogue. The 100k pot allows this circuit to trigger over a wide range of temperatures. A slight amount of hysteresis is provided by inclusion of the 270k resistor. This prevents relay chatter when temperature is near the switching threshold of this circuit __ Designed by Andy Collison

Full-Bridge Amplification using a Single Amplifier - This example shows a single amplifier being used to produce single-ended gain. This topology is best used in applications where the gain setting resistor can be made to match the temperature coefficient of the strain gauges. if the bridge is composed of precision resistors, with only one or two variable elements, the reference __ Linear Technology/Analog Devices App Note, Apr 29th 2010

Full-Bridge Amplification using Autozero Amplifiers to Reduce Input Referred Noise - This circuit shows an example of a simple amplification scheme. This example produces a differential output with a common mode voltage of 2.5V, as determined by the bridge. The use of a true three amplifier instrumentation amplifier is not necessary, as the LTC2430/LTC2431 have common mode rejection far beyond that of most __ Linear Technology/Analog Devices App Note, Apr 29th 2010

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